Understanding rebase

What properties must commits have for them to be rebase-able?

One example arrangement that would cause a rebase to fail is:

- change lines 10, 12, 14 in branch A
- change lines 11, 13, 15 in branch B

These changes are commutative (I believe), but that is insufficient for 
avoiding conflicts on a rebaes.  For a concrete example of this, see:

http://assorted.svn.sourceforge.net/viewvc/assorted/sandbox/trunk/src/git/gitsvn.bash?revision=1065&view=markup

Another question that probably gets at the same thing: I understand what 
rebasing gives me from a high level (rearranging a branch of commits to 
be in a series with another branch), but is there a simple explanation 
of how, precisely, this is accomplished?

Thanks in advance!
-- 
Yang Zhang
http://www.mit.edu/~y_z/